1. Field of the Invention
The present invention relates to a base station apparatus and a method for setting the radio communication parameters, and particularly to a base station apparatus of multiple access method in which a plurality of users make the communications at the same time by sharing a radio channel, and a method for setting the temporary radio communication parameters.
2. Description of the Related Art
As the multiple access methods in which a plurality of users make the communications by sharing a radio channel, a code division multiple access (CDMA), a time division multiple access (TDMA) and a frequency division multiple access (FDMA) are well known.
For example, in a communication system of code division multiple access method in which the same frequency band is shared among a plurality of communication waves, individual communication waves are distinguished by the spreading codes of random code series. As the spreading code is better in the detection characteristic (auto-correlation characteristic) and the identification characteristic (cross-correlation characteristic) between different spreading codes, the system efficiency is improved. Therefore, all the random combinations of codes determined by the series length are not employed, but the code series to attain the required characteristics are selectively employed. Accordingly, when the high system efficiency is required, the spreading code is limited and the assignable number of spreading codes is below the total number of simultaneous communication waves supposed for the system.
Particularly in the satellite downlink of a W-CDMA (Wideband CDMA) cellular system, the spreading code used is demanded to have the code orthogonality capable of reducing mutual interference between different spreading codes, in addition to the high detection characteristic and identification characteristic, to implement high quality communications even at low transmission power. Therefore, the assignable number of spreading codes is smaller than in the satellite uplink. This small number of spreading codes is repeatedly employed for effective use, but a different code for each cell is employed and superimposed to prevent radio interference between cells.
In the W-CDMA cellular system, the spreading code for actually spreading the user data in the broadband is called a channelization code, and the code for preventing radio interference between cells superimposed for each cell is called a scrambling code.
The number of scrambling codes to distinguish between the cells is not unlimited, in which only 512 kinds are defined in the W-CDMA cellular system. It is necessary that the scrambling code of same kind is not employed in proximity to prevent radio interference.
In the general cellular system, the arrival area of electric wave was estimated for each base station by a computer simulation in which the position of a base station apparatus (herein after simply referred to as a base station) for forming the cell and the apparatus and antenna construction are set up, and the radio network designer manually made the settings so that the scrambling code of same kind may not be set to the base stations in which the arrival areas overlap with the aid of a computer. Therefore, when a new base station was installed corresponding to increased traffic, the designer had to make the settings again.
Also, since the scrambling code is set up based on the estimation of the computer simulation, a radio interference occurs between the scrambling codes of same kind, when there is an error between the actual field and the wave arrival area, whereby it is required to make the settings again. Accordingly, these operations take a lot of time, a labor of the designer, and a trouble of the field confirmor.
There is a technique that the base station autonomously sets up the spreading code (e.g., JP2005-175611A). Also, another technique in which the mobile station acquires the information of the base station, and makes a report to the base station to which the self station is connected, and the base station automatically updates the information was described in JP2001-54158A.